13 Lac-Operon AnalogyLike an elephant that likes to sit on a railroad track blocking the train.The only thing that the elephant likes better than to sit on his spot on the track is peanuts.If peanuts are available, the elephant leaves the track and eats the peanuts.While he is gone the train can proceed down the track until the elephant goes back to sit on the track after eating all the peanuts.
14 Controls in Eukaryotic Cells Control of transcriptionTranscript processing controlsControls over translationControls following translation
15 Most Genes Are Turned Off Cells of a multicelled organism rarely use more than 5-10 percent of their genes at any given timeThe remaining genes are selectively expressed
16 Homeotic Genes Occur in all eukaryotes Master genes that control development of body partsEncode homeodomains (regulatory proteins)Homeobox sequence can bind to promoters and enhancers
17 X Chromosome Inactivation One X inactivated in each cell of femaleCreates a “mosaic” for X chromosomesGoverned by XIST geneFigure 15.6 Page 245
18 Hormones Signaling molecules Stimulate or inhibit activity in target cellsMechanism of action variesMay bind to cell surfaceMay enter cell and bind to regulatory proteinsMay bind with enhancers in DNA
19 Vertebrate Hormones Some have widespread effects Somatotropin (growth hormone)Others signal only certain cells at certain timesProlactin stimulates milk production
20 Phytochrome Signaling molecule in plants Activated by red wavelengths, inactivated by far-red wavelengthsChanges in phytochrome activity influence transcription of certain genes
21 Controlling the Cell Cycle Cycle has built-in checkpointsProteins monitor chromosome structure, whether conditions favor division, etc.Proteins are products of checkpoint genesKinasesGrowth factors
22 Oncogenes Have potential to induce cancer Mutated forms of normal genesCan form following insertions of viral DNA into DNA or after carcinogens change the DNA
23 Cancer Characteristics Plasma membrane and cytoplasm alteredCells grow and divide abnormallyWeakened capacity for adhesionLethal unless eradicated
24 Apoptosis Programmed cell death Signals unleash molecular weapons of self-destructionCancer cells do not commit suicide on cue
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